Information Coding, Number Systems, and Measurement of Information
Core ideas
Computers store everything in binary. Candidates must convert between binary, decimal, octal, and hexadecimal, and measure information in bits and bytes (1 byte = 8 bits; 1 KiB = 1024 bytes). Text coding (ASCII, Unicode), and the idea that n bits encode 2ⁿ distinct values, are central.
Traps to watch
- Using 1000 instead of 1024 for KiB/MiB, or mixing bits and bytes (a 2 Mbit file is 256 KiB, not 2 MiB).
- Forgetting that character count × bits per character gives total bits, then divide by 8 for bytes.
- Off-by-one in range questions: n bits represent 0 to 2ⁿ−1 (unsigned), so 8 bits give 0–255, i.e. 256 values.
- Converting hex digits individually to decimal instead of to 4-bit groups.
Rule of thumb
For "how many bits to encode N objects?" find the smallest n with 2ⁿ ≥ N. For unit conversions, write the chain (bits → bytes → KiB → MiB) and cancel units explicitly.
Worked example
A text of 512 characters uses a 16-bit encoding. Total = 512 × 16 = 8192 bits = 1024 bytes = 1 KiB. If the question asks for bytes, the answer is 1024, not 8192 - always check the requested unit.